1. Technical Field
The invention relates generally to communication systems; and, more particularly, it relates to communication systems that seek to perform frequency drift and phase error compensation in receivers that employing vector orthogonal frequency division multiplexing (VOFDM).
2. Related Art
Communication systems transmit digital data through imperfect communication channels. These symbols may undergo some undesirable corruption due to the imperfection of the communication channel. One effort to try to avoid such situations is focused on performing forward error correction (FEC) coding. However, there is typically some difficulty in extracting the information contained within these symbols after they have been undesirably altered within the communication channel. There exist some methods that seek to curb the effect that the communication channel has had on the data; one such method includes employing using Decision Feedback Equalizers (DFEs). However, even after the incoming signal has been equalized, the extraction of the data, that has undergone some alteration due to the channel effects, is still a probabilistic determination.
To further complicate the issue, the source signal that provides the data that are received by a receiver within the communication system may sometimes undergo undesirable frequency drift. The effect can be phase error and/or frequency drift in the received data, thereby making the extraction of the data even that much more difficult at the receiver end. Typically, data are transmitted using bursts (a number of symbols) that have a frequency and phase error. Prior art receiver systems typically assume that any phase error is fixed during a received frame of data. However, frequency drift and phase error may actually exist within the very frame that is being demodulated and decoded.
One prior art approach is to simply calculate an average phase for the given frame. For example, in a prior art receiver, the incoming signal is phase compensated (in a frequency tracking operation) to translate each received frame according to the average error determined during the frame. In the prior art receiver, the average frequency and phase error is determined based upon prior frames and applied to the current received frame. The deficiency of the prior art method is clear; if there is frequency drift and phase error within the current frame, then this prior art form of compensation will not sufficiently compensate for error within the current frame. As is typically the case, the frequency and phase error is not fixed during the frame; moreover, it is not most-accurately predicted based upon prior frames.
While the average phase error is estimated for the current block with the benefit of the current block, the frequency error on the other hand (which causes a ramp of phase error across the frame), is only being estimated using past frames, and does not benefit from observation of the current frame. Thus, the prior art receiver suffers in its operation due to erroneous frequency and phase compensation, causing errors in data demodulation and subsequent decoding.
Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the invention as set forth in the remainder of the present application with reference to the drawings.